As shown in FIG. 1 a conventional adjuster track assembly 1 for a vehicle seat has at least one stationary lower rail 2 connected to the vehicle floor via corresponding brackets 21, 22 and a movable upper rail 3 for receiving a vehicle seat via rear and front rockers 31, 32. The upper rail 3 and the lower rail 2 are embodied essentially as U-profiles. They are arranged here with respect to one another so that an essentially rectangular cross-sectional profile results. The lower rail 2 and the upper rail 3, viewed in cross-section each have two legs curved at the ends such that the upper rail 3 is guided in the lower rail 2 so as to be displaceable along the lower rail 2 in a forward and backward direction indicated by arrows A. Positioning of the vehicle seat in the longitudinal direction of the vehicle body can thus be adjusted by sliding the upper rail 3 along the lower rail 2. Between the lower rail 2 and the upper rail 3, there is interposed a lock means 10 for regulating the movement of the upper rail 3 along the lower rail 2.
A horizontal leg 20 of the lower rail 2 that forms the bottom of the rectangular profile, and a vertical leg 30 of the upper rail 3 that forms the first side wall of the rectangular profile, engage around one another with their ends and form a lower bearing region. A bearing element 4 for linear guidance and support of the upper rail 3 is provided between the curved ends of the horizontal leg 20 of the lower rail 2 and the vertical leg 30 of the upper rail 3. According to FIG. 2 illustrating the bearing element 4 in different perspective views the bearing element 4 comprises a vertical leg 41 adapted to the vertical leg 20 of the lower rail 2 and a horizontal leg 42 adapted to the vertical leg 30 of the upper rail 3.
The curved end of the vertical leg 41 of the bearing element 4 includes upper bearing cages 43 with rollers 7 whereas the horizontal leg 42 of the bearing element 4 includes lower bearing cages 44 which according to FIGS. 3-5 comprise roller pockets 6 and rollers 8 accommodated therein.
When the upper rail 3 is displaced relative to the lower rail 2, the bearing element 4 with its bearing cages 43, 44 is carried along with the upper rail 3. During this process, the bearing element 4 supports the upper rail 3 on the lower rail 2 by means of rollers 7, 8 accommodated within roller pockets of the bearing cages 43, 44. According to the cross-section along the section line IV-IV in FIG. 3 shown in FIG. 4 and the enlarged illustration of FIG. 5 depicting a section of the lower bearing cages 44 the rollers 8 are retained both in the forward and backward direction, i.e. in the longitudinal adjustment direction of the adjuster track assembly, within concaved valleys 61, 62 of the roller pockets 6 and between side walls 63, 64 of the roller pockets 6 in the cross-car direction, i.e. perpendicular to the longitudinal adjustment direction of the adjuster track assembly.
Typically, in such an adjustment mechanism of a vehicle seat two lower rails are arranged parallel to one another in the longitudinal direction of the vehicle, whereby the vehicle seat is fastened to the two upper rails displaceably mounted in their corresponding lower rails.
In the adjuster track assembly the bearing cages 43, 44 are designed to allow for the upper and lower rails 2, 3 to move within a defined track effort range. Once the upper and lower rails 2, 3 are mated to form the rail kit, they undergo a break-in cycle. This operation cycles the upper rail 3 in the forward and backward direction through the functional travel range to ensure proper distribution of grease throughout all moving components.
During the initial break-in cycle the rollers 7, 8 rotate according to the arrows B of FIG. 5 and begin to remove sections of an electrophoretic anticorrosive coating for protecting the upper and lower rail 2, 3 against corrosion from the contact surface of the upper and lower rail 2, 3 as well as plastic or metal shavings or abrasions of the bearing element 4. The paint particles and shavings follow the flow of grease and get lodged as debris and abrasions D into the roller pockets 6 of the lower bearing cages 44, in particular. This causes increased rotational efforts or even a complete binding of the rollers 82 accommodated in the roller pockets 6 of the lower bearing cages 44. This results in high track efforts, leading to a higher number of rejected parts and quality as well as warranty issues.